(1) Field of the invention
The present invention relates to a system and method for controlling a damping force characteristic of a shock absorber (hereinafter referred to as a damper) installed between an unsprung mass and a sprung mass of an automotive vehicle and particularly relates to the controlling system and method with a countermeasure against noise signals.
(2) Description of the Background Art
Japanese Patent Application First (unexamined) Publication No. Showa 61-163011 exemplifies a previously proposed damping force controlling system with the countermeasure against noise signals.
The disclosed previously proposed damping force controlling system generally includes: damping force detecting means for detecting a damping force of the vehicular damper; relative displacement calculating means for calculating a relative displacement between a vehicular body and tire wheel from a detected damping force; road running state determining means for determining a state of the road on which the vehicle runs according to a period of the relative displacement which is larger than a predetermined displacement from the calculated relative displacement; and damping force switching means for switching the damping force of the damper in response to a signal derived from the road state determining means.
That is to say, the damping force of the vehicular damper is detected by the damping force detecting means and the relative displacement between the vehicular body and tire wheel is estimated by the relative displacement calculating means.
Then, a controller determines whether the road condition is paved or rough according to a period during which a larger displacement occurs than a predetermined displacement from the estimated relative displacement and a damping force of the damper is switched by means of the damping force switching means. Thereby, the road surface condition such as paved road, rough road, and projection is determined so that an appropriate damping force control according to a road surface condition can be carried out.
However, in such a previously proposed damping force controlling system as described above, the determination of the road surface condition such as paved road, rough road, and projection is carried out by the comparison of the relative displacement between a tire wheel and vehicular body with a stationary predetermined reference quantity so that a condition in which the calculated displacement exceeds the reference quantity is maintained when the vehicle turns or zigzags.
Therefore, the appropriate damping force control according to the running road surface condition is not carried out so that a vehicular comfort and steering stability are reduced.